The present invention relates to the general field of gas turbine casings, and more particularly holding casings of gas turbine fans for aeronautical engines.
In a gas turbine aeronautical engine, a fan casing fulfils a number of functions. It defines the incoming air stream to the engine, supports abradable material with respect to the tip of the fan vanes, supports an optional structure for sound wave absorption for acoustic inlet treatment of the engine and incorporates or supports a holding shield. The latter comprises a trap for catching debris such as ingested items or fragments of damaged vanes thrown out by centrifuge action to prevent them from passing through the casing and reaching other parts of the aircraft.
Making a casing for holding a fan made of composite material has already been proposed. Reference could be made to document EP 1 961 923 which describes the production of a casing made of composite material of evolutive thickness, comprising the formation of a fibrous reinforcement by superposed layers of a fibrous texture and densification of the fibrous reinforcement by a matrix. According to this invention, the fibrous texture is made by three-dimensional weaving with evolutive thickness and is wound in several superposed layers onto a mandrel having a central wall of profile corresponding to that of the casing to be manufactured and two lateral flanges of profile corresponding to those of the external flanges of the casing. The resulting fibrous preform is held on the mandrel and impregnation by resin is completed under vacuum prior to polymerisation. The winding on a mandrel of a woven texture of evolutive thickness as described in this document directly gives a tubular preform having the preferred profile with variable thickness.
In practice, carrying out this process poses the problem of holding the fibrous preform during its winding on the mandrel. During this winding, sufficient traction force should indeed be exerted on each layer of fibrous texture to ensure effective compaction of the letter. This requires in particular that the first layer of fibrous texture which is wound on the mandrel be correctly packed up against the latter before successive layers are wound on.
For this purpose, document FR 2 945 573 discloses an impregnation mandrel in which the hooking of the first layer of fibrous texture is done by a removable plate fitted with points which penetrate the layer of fibrous texture. Even though efficacious, this type of hooking can have the risk of seeing the points of the plate damage the fibrous preform if a too strong winding tension is applied on the latter.